Many humans lose the ability to digest milk after childhood. And essentially all non-human mammals lose this ability after weaning. This suggests the ability of humans to digest lactose in dairy products is actually a quirk of nature or adaptation.
Lactose intolerance varies by ethnic origin. Asian and first nations people are almost 100% intolerant, African origin 60 to 80%, South American 50 to 80% and those of European origin about 20%. Worldwide, approximately 75% of people are lactose intolerant.
What is lactose intolerance?
Lactose is a complex sugar (two smaller sugars attached together) and it needs to be broken down into two simple sugars so it can be absorbed. This is done by an enzyme called lactase.
Because lactose is a sugar, if it’s not absorbed, it becomes food for bacteria in the large intestine. When these bacteria consume sugars, they produce gas. This “air” in the intestine causes the cramps, bloating, flatulence and abdominal pain that are associated with lactose intolerance. The extra lactose sugar also draws water into the bowel causing diarrhea if enough is consumed.
A quick genetic lesson
DNA is composed of genes. Each gene is a code or template for a protein that has a particular action in the body. For example, there are genetic codes to make light detecting proteins in the eyes, and oxygen carrying proteins in the blood. Every cell has a complete copy of your DNA. Individual genes in the DNA are turned on or off as necessary so only the proteins that are needed are produced in each part of the body. This is done by “epigenetic modification” – chemicals inside the cells bind to the gene, blocking it from making its protein. Epigenetic modification of the lactase gene, to turn it off once past childhood, does not happen in lactose tolerate people.
Lactose tolerance is relatively new, in terms of evolution. It is believed to have started around the same time as dairy animals were first domesticated. The change that occurs to prevent lactose intolerance isn’t to the lactase gene itself but to a nearby area of DNA that protects against the normal “turning off” of the gene.
However, if the small intestine is damaged by disease or if large doses of antibiotics are given, a person who was lactose-tolerant can become intolerant later in life.
Microbiome and lactose intolerance
When scientists noticed that antibiotics could create lactose intolerance, they began to investigate whether the bacteria (microbiome) in the intestine had an effect on the lactase gene or on lactose intolerance in general.
Their studies showed that symptoms of lactose intolerance can be relieved in some people by increasing lactose-digesting bacteria in their small intestine. These microbes eat the lactose but produce lactic acid instead of gas. Lactic acid does not produce the unpleasant symptoms of lactose intolerance, and this is one way that some people can tolerate dairy foods without actually producing lactase enzyme. The microbiome tends to be similar in populations, since bacteria are passed from person to person, so it might be part of the explanation of how certain areas have less lactose intolerance than others.
One way to promote the growth of lactic acid producing bacteria in the digestive system, is to “feed” it a complex sugar (or “prebiotic”) it can digest but humans cannot. Studies to find an effective prebiotic that could be produced commercially are in progress.
However, there are many fermented foods available – like yoghurt, kefir, sauerkraut and other pickled vegetables – that can introduce new microbes into the digestive system. While there are no guarantees they will contain bacteria that like to consume lactose, they are a healthy addition to any diet that may improve digestion. Researchers suggest 5 servings weekly that include at least 3 different types of fermented foods.
Do we really need dairy products?
There is an ongoing debate: if we evolved to be unable to digest dairy products as adults, do we really need these foods to be healthy? The nay-sayers point out that many populations (and animals) never drink milk as adults, and we know that many just cannot tolerate it. The pro-milk group tell us about the many nutrients it contains in foods that are easy to consume.
Recent research has found that consuming milk or calcium supplements as an adult does not reduce the chance of a bone fracture. And much of bones’ strength is developed early in life. But milk products do contain many other nutrients and are, overall, healthy foods to consume. Geneticists note that, because the ability to tolerate lactose has increased dramatically in populations who consume dairy products, it must confer an advantage for survival… over centuries, those who ate it (on average) lived longer and had more descendants than those who could not.
So, if you are unable to digest the lactose in dairy products, try improving the health of your gut microbiome with prebiotics and probiotics. If you’re lucky you may be able to increase the microbes that can improve your tolerance to these foods. Remember that the lactose in fermented dairy products, like kefir, yoghurt or cheese, has been mostly digested in the fermentation process, so is easier to tolerate for those who do not produce their own lactase enzyme. And you can always take lactase enzyme as a supplement – it’s available commercially (LactaidÒ) in forms that can be mixed with food to pre-digest it or it can be taken along with lactose-containing food.
After all... what is life without ice cream or cheese?
References:
National Institutes of Health: Prebiotics for lactose intolerance
Study: Improving lactose digestion and symptoms of lactose intolerance with a novel galacto-oligosaccharide
